Methods and arrangements for controlling the speed of vehicles are known from the state of the art in many variations. For example, SAE Paper No. 961010 entitled "Adaptive Cruise Control, System Aspects and Development Trends" (1996) discloses a road-speed controller which takes into account the distance to the vehicle ahead. The driver inputs the desired speed of the vehicle via an operator adjustable lever with the functions which are customary for road-speed controllers, such as set speed, resume speed, accelerate, et cetera. The desired speed is controlled in a manner comparable to a conventional vehicle road-speed controller when a forward vehicle is not present in that a desired acceleration is computed from the difference between the desired and driving speeds. If a radar system detects a forward vehicle, then the distance and the relative speed to this vehicle are determined. The control task in this case is that the relative speed is controlled to zero and simultaneously a desired spacing is maintained which is dependent upon speed. Parameters for determining the desired distance (time gap) are adjustable by the driver. This follow-up controller determines a desired acceleration from the above-mentioned variables. The desired acceleration is, however, limited by the desired acceleration of the road-speed control component so that the pregiven desired speed cannot be exceeded even in the follow-up control. Distance controllers and speed controllers provide desired values for the acceleration and deceleration, respectively, of the vehicle in dependence upon the operating state. These desired values are adjusted by influencing the engine of the vehicle and/or the brakes.
German patent publication 4,338,399 discloses a road-speed controller wherein a desired acceleration of the vehicle is computed on the basis of the difference between the desired and actual speeds. This computed desired acceleration serves as the basis of the vehicle control. The actual acceleration of the vehicle is controlled by controlling the engine and/or by actuating the wheel brakes of the vehicle in such a manner that it approaches the desired acceleration.
The configuration of a controller of this kind defines a compromise between rapid reaction to the input data and dragging reaction in order not to confuse the driver or make the driver insecure and/or to maintain comfort. For this reason, and as a rule, the acceleration and/or the acceleration change is significantly throttled compared to the possibilities of the vehicle. In this way, the acceleration and/or the change of the acceleration of the vehicle is limited; that is, it is not possible for the actual acceleration and/or acceleration change of the vehicle to exceed this limit. Accordingly, the vehicle does not accelerate faster than pregiven by the limit value. Here, the problem occurs that the acceleration dynamic of the controller often lies significantly below the expectation of the driver, for example, when the forward driver is highly accelerating or where there is a passing maneuver or a swerving maneuver.